1. Field of the Invention
The invention relates to methods for image characterization and image search, particularly for search in image database comprising large data amount, in order to improve search efficiency and accuracy.
2. Description of the Related Art
Conventionally, images are recorded in RGB format. While establishing image database, first the color histograms of images are extracted. Then image search is performed on the color histogram. FIG. 1A shows a color histogram. The horizontal axis represents the color level (generally from 0 to 255) and the vertical axis represents the ratio of the pixel amount. The ratio of the pixel amount is calculated by the amount of pixels in certain level divided with the total amount of overall pixels, and is range from 0 to 1. The three curves R, G and B represent the distribution of the three primary colors within an image from dark to light. Using color histogram has many advantages. For example, the extraction is easy and very efficient. In addition, the image characteristics may still remain invariant after translation and/or rotation.
FIG. 1B shows a method for extracting image characteristics. In step 101, first, an original image is inputted. In step 103, color distribution is calculated for each pixel to generate a color histogram, similar to that shown in FIG. 1A. In step 105, the characteristics of the image are finally determined according to the color histogram for performing later search. The method has drawbacks that the color histogram may not be able to reflect the spatial distribution due to its insensitiveness to the variations of image direction and image size. If two different images have similar color histograms, search might come up with error result.
It is therefore a desire need to provide improved methods for image characterization and image search.